1
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Gong T, McNally KL, Konanoor S, Peraza A, Bailey C, Redemann S, McNally FJ. Roles of Tubulin Concentration during Prometaphase and Ran-GTP during Anaphase of Caenorhabditis elegans Meiosis. Life Sci Alliance 2024; 7:e202402884. [PMID: 38960623 PMCID: PMC11222656 DOI: 10.26508/lsa.202402884] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2024] [Revised: 06/25/2024] [Accepted: 06/26/2024] [Indexed: 07/05/2024] Open
Abstract
In many animal species, the oocyte meiotic spindle, which is required for chromosome segregation, forms without centrosomes. In some systems, Ran-GEF on chromatin initiates spindle assembly. We found that in Caenorhabditis elegans oocytes, endogenously-tagged Ran-GEF dissociates from chromatin during spindle assembly but re-associates during meiotic anaphase. Meiotic spindle assembly occurred after auxin-induced degradation of Ran-GEF, but anaphase I was faster than controls and extrusion of the first polar body frequently failed. In search of a possible alternative pathway for spindle assembly, we found that soluble tubulin concentrates in the nuclear volume during germinal vesicle breakdown. We found that the concentration of soluble tubulin in the metaphase spindle region is enclosed by ER sheets which exclude cytoplasmic organelles including mitochondria and yolk granules. Measurement of the volume occupied by yolk granules and mitochondria indicated that volume exclusion would be sufficient to explain the concentration of tubulin in the spindle volume. We suggest that this concentration of soluble tubulin may be a redundant mechanism promoting spindle assembly near chromosomes.
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Affiliation(s)
- Ting Gong
- https://ror.org/05rrcem69 Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
| | - Karen L McNally
- https://ror.org/05rrcem69 Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
| | - Siri Konanoor
- https://ror.org/05rrcem69 Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
| | - Alma Peraza
- https://ror.org/05rrcem69 Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
| | - Cynthia Bailey
- https://ror.org/05rrcem69 Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
| | - Stefanie Redemann
- https://ror.org/0153tk833 Department of Cell Biology, University of Virginia, School of Medicine, Charlottesville, VA, USA
| | - Francis J McNally
- https://ror.org/05rrcem69 Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
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2
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Gong T, McNally KL, Konanoor S, Peraza A, Bailey C, Redemann S, McNally FJ. Roles of Tubulin Concentration during Prometaphase and Ran-GTP during Anaphase of C. elegans meiosis. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.19.590357. [PMID: 38659754 PMCID: PMC11042349 DOI: 10.1101/2024.04.19.590357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/26/2024]
Abstract
In many animal species, the oocyte meiotic spindle, which is required for chromosome segregation, forms without centrosomes. In some systems, Ran-GEF on chromatin initiates spindle assembly. We found that in C. elegans oocytes, endogenously-tagged Ran-GEF dissociates from chromatin during spindle assembly but re-associates during meiotic anaphase. Meiotic spindle assembly occurred after auxin-induced degradation of Ran-GEF but anaphase I was faster than controls and extrusion of the first polar body frequently failed. In search of a possible alternative pathway for spindle assembly, we found that soluble tubulin concentrates in the nuclear volume during germinal vesicle breakdown. We found that the concentration of soluble tubulin in the metaphase spindle region is enclosed by ER sheets which exclude cytoplasmic organelles including mitochondria and yolk granules. Measurement of the volume occupied by yolk granules and mitochondria indicated that volume exclusion would be sufficient to explain the concentration of tubulin in the spindle volume. We suggest that this concentration of soluble tubulin may be a redundant mechanism promoting spindle assembly near chromosomes.
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3
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Torisawa T, Kimura A. Sequential accumulation of dynein and its regulatory proteins at the spindle region in the Caenorhabditis elegans embryo. Sci Rep 2022; 12:11740. [PMID: 35817834 PMCID: PMC9273622 DOI: 10.1038/s41598-022-15042-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 06/16/2022] [Indexed: 11/09/2022] Open
Abstract
Cytoplasmic dynein is responsible for various cellular processes during the cell cycle. The mechanism by which its activity is regulated spatially and temporarily inside the cell remains elusive. There are various regulatory proteins of dynein, including dynactin, NDEL1/NUD-2, and LIS1. Characterizing the spatiotemporal localization of regulatory proteins in vivo will aid understanding of the cellular regulation of dynein. Here, we focused on spindle formation in the Caenorhabditis elegans early embryo, wherein dynein and its regulatory proteins translocated from the cytoplasm to the spindle region upon nuclear envelope breakdown (NEBD). We found that (i) a limited set of dynein regulatory proteins accumulated in the spindle region, (ii) the spatial localization patterns were distinct among the regulators, and (iii) the regulatory proteins did not accumulate in the spindle region simultaneously but sequentially. Furthermore, the accumulation of NUD-2 was unique among the regulators. NUD-2 started to accumulate before NEBD (pre-NEBD accumulation), and exhibited the highest enrichment compared to the cytoplasmic concentration. Using a protein injection approach, we revealed that the C-terminal helix of NUD-2 was responsible for pre-NEBD accumulation. These findings suggest a fine temporal control of the subcellular localization of regulatory proteins.
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Affiliation(s)
- Takayuki Torisawa
- Cell Architecture Laboratory, National Institute of Genetics, Mishima, Japan.,Department of Genetics, The Graduate University for Advanced Studies, Sokendai, Mishima, Japan
| | - Akatsuki Kimura
- Cell Architecture Laboratory, National Institute of Genetics, Mishima, Japan. .,Department of Genetics, The Graduate University for Advanced Studies, Sokendai, Mishima, Japan.
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4
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When Down Is Up: Heterochromatin, Nuclear Organization and X Upregulation. Cells 2021; 10:cells10123416. [PMID: 34943924 PMCID: PMC8700316 DOI: 10.3390/cells10123416] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2021] [Revised: 11/29/2021] [Accepted: 12/01/2021] [Indexed: 12/21/2022] Open
Abstract
Organisms with highly differentiated sex chromosomes face an imbalance in X-linked gene dosage. Male Drosophila solve this problem by increasing expression from virtually every gene on their single X chromosome, a process known as dosage compensation. This involves a ribonucleoprotein complex that is recruited to active, X-linked genes to remodel chromatin and increase expression. Interestingly, the male X chromosome is also enriched for several proteins associated with heterochromatin. Furthermore, the polytenized male X is selectively disrupted by the loss of factors involved in repression, silencing, heterochromatin formation or chromatin remodeling. Mutations in many of these factors preferentially reduce male survival or enhance the lethality of mutations that prevent normal recognition of the X chromosome. The involvement of primarily repressive factors in a process that elevates expression has long been puzzling. Interestingly, recent work suggests that the siRNA pathway, often associated with heterochromatin formation and repression, also helps the dosage compensation machinery identify the X chromosome. In light of this finding, we revisit the evidence that links nuclear organization and heterochromatin to regulation of the male X chromosome.
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5
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Larouche M, Kachaner D, Wang P, Normandin K, Garrido D, Yao C, Cormier M, Johansen KM, Johansen J, Archambault V. Spatiotemporal coordination of Greatwall-Endos-PP2A promotes mitotic progression. J Cell Biol 2021; 220:211965. [PMID: 33836042 PMCID: PMC8042607 DOI: 10.1083/jcb.202008145] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2020] [Revised: 02/17/2021] [Accepted: 03/08/2021] [Indexed: 12/31/2022] Open
Abstract
Mitotic entry involves inhibition of protein phosphatase 2A bound to its B55/Tws regulatory subunit (PP2A-B55/Tws), which dephosphorylates substrates of mitotic kinases. This inhibition is induced when Greatwall phosphorylates Endos, turning it into an inhibitor of PP2A-Tws. How this mechanism operates spatiotemporally in the cell is incompletely understood. We previously reported that the nuclear export of Greatwall in prophase promotes mitotic progression. Here, we examine the importance of the localized activities of PP2A-Tws and Endos for mitotic regulation. We find that Tws shuttles through the nucleus via a conserved nuclear localization signal (NLS), but expression of Tws in the cytoplasm and not in the nucleus rescues the development of tws mutants. Moreover, we show that Endos must be in the cytoplasm before nuclear envelope breakdown (NEBD) to be efficiently phosphorylated by Greatwall and to bind and inhibit PP2A-Tws. Disrupting the cytoplasmic function of Endos before NEBD results in subsequent mitotic defects. Evidence suggests that this spatiotemporal regulation is conserved in humans.
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Affiliation(s)
- Myreille Larouche
- Institute for Research in Immunology and Cancer, Université de Montréal, Montreal, Quebec, Canada.,Department of Biochemistry and Molecular Medicine, Université de Montréal, Montreal, Quebec, Canada
| | - David Kachaner
- Institute for Research in Immunology and Cancer, Université de Montréal, Montreal, Quebec, Canada.,Department of Biochemistry and Molecular Medicine, Université de Montréal, Montreal, Quebec, Canada
| | - Peng Wang
- Institute for Research in Immunology and Cancer, Université de Montréal, Montreal, Quebec, Canada.,Department of Biochemistry and Molecular Medicine, Université de Montréal, Montreal, Quebec, Canada
| | - Karine Normandin
- Institute for Research in Immunology and Cancer, Université de Montréal, Montreal, Quebec, Canada
| | - Damien Garrido
- Institute for Research in Immunology and Cancer, Université de Montréal, Montreal, Quebec, Canada.,Department of Biochemistry and Molecular Medicine, Université de Montréal, Montreal, Quebec, Canada
| | - Changfu Yao
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA
| | - Maxime Cormier
- Institute for Research in Immunology and Cancer, Université de Montréal, Montreal, Quebec, Canada
| | - Kristen M Johansen
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA
| | - Jørgen Johansen
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA
| | - Vincent Archambault
- Institute for Research in Immunology and Cancer, Université de Montréal, Montreal, Quebec, Canada.,Department of Biochemistry and Molecular Medicine, Université de Montréal, Montreal, Quebec, Canada
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6
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Métivier M, Gallaud E, Thomas A, Pascal A, Gagné JP, Poirier GG, Chrétien D, Gibeaux R, Richard-Parpaillon L, Benaud C, Giet R. Drosophila Tubulin-Specific Chaperone E Recruits Tubulin around Chromatin to Promote Mitotic Spindle Assembly. Curr Biol 2021; 31:684-695.e6. [PMID: 33259793 DOI: 10.1016/j.cub.2020.11.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2020] [Revised: 09/29/2020] [Accepted: 11/03/2020] [Indexed: 12/31/2022]
Abstract
Proper assembly of mitotic spindles requires microtubule nucleation not only at the centrosomes but also around chromatin. In this study, we found that the Drosophila tubulin-specific chaperone dTBCE is required for the enrichment of tubulin in the nuclear space after nuclear envelope breakdown and for subsequent promotion of spindle microtubule nucleation. These events depend on the CAP-Gly motif found in dTBCE and are regulated by Ran and lamin proteins. Our data suggest that during early mitosis, dTBCE and nuclear pore proteins become enriched in the nucleus, where they interact with the Ran GTPase to promote dynamic tubulin enrichment. We propose that this novel mechanism enhances microtubule nucleation around chromatin, thereby facilitating mitotic spindle assembly.
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Affiliation(s)
- Mathieu Métivier
- Univ Rennes, CNRS, IGDR (Institut de Génétique et Développement de Rennes) - UMR 6290, F-35000 Rennes, France
| | - Emmanuel Gallaud
- Univ Rennes, CNRS, IGDR (Institut de Génétique et Développement de Rennes) - UMR 6290, F-35000 Rennes, France
| | - Alexandre Thomas
- Univ Rennes, CNRS, IGDR (Institut de Génétique et Développement de Rennes) - UMR 6290, F-35000 Rennes, France
| | - Aude Pascal
- Univ Rennes, CNRS, IGDR (Institut de Génétique et Développement de Rennes) - UMR 6290, F-35000 Rennes, France
| | - Jean-Philippe Gagné
- Centre de Recherche du Centre Hospitalier Universitaire de Québec - Pavillon CHUL, Université Laval, Québec City, QC, Canada
| | - Guy G Poirier
- Centre de Recherche du Centre Hospitalier Universitaire de Québec - Pavillon CHUL, Université Laval, Québec City, QC, Canada
| | - Denis Chrétien
- Univ Rennes, CNRS, IGDR (Institut de Génétique et Développement de Rennes) - UMR 6290, F-35000 Rennes, France
| | - Romain Gibeaux
- Univ Rennes, CNRS, IGDR (Institut de Génétique et Développement de Rennes) - UMR 6290, F-35000 Rennes, France
| | - Laurent Richard-Parpaillon
- Univ Rennes, CNRS, IGDR (Institut de Génétique et Développement de Rennes) - UMR 6290, F-35000 Rennes, France
| | - Christelle Benaud
- Univ Rennes, CNRS, IGDR (Institut de Génétique et Développement de Rennes) - UMR 6290, F-35000 Rennes, France
| | - Régis Giet
- Univ Rennes, CNRS, IGDR (Institut de Génétique et Développement de Rennes) - UMR 6290, F-35000 Rennes, France.
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7
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Dey G, Baum B. Nuclear envelope remodelling during mitosis. Curr Opin Cell Biol 2021; 70:67-74. [PMID: 33421755 PMCID: PMC8129912 DOI: 10.1016/j.ceb.2020.12.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 12/07/2020] [Accepted: 12/09/2020] [Indexed: 12/20/2022]
Abstract
The defining feature of the eukaryotic cell, the nucleus, is bounded by a double envelope. This envelope and the nuclear pores within it play a critical role in separating the genome from the cytoplasm. It also presents cells with a challenge. How are cells to remodel the nuclear compartment boundary during mitosis without compromising nuclear function? In the two billion years since the emergence of the first cells with a nucleus, eukaryotes have evolved a range of strategies to do this. At one extreme, the nucleus is disassembled upon entry into mitosis and then reassembled anew in the two daughter cells. At the other, cells maintain an intact nuclear compartment boundary throughout the division process. In this review, we discuss common features of the division process that underpin remodelling mechanisms, the topological challenges involved and speculate on the selective pressures that may drive the evolution of distinct modes of division.
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Affiliation(s)
- Gautam Dey
- Cell Biology and Biophysics, European Molecular Biology Laboratory, 69117, Heidelberg, Germany.
| | - Buzz Baum
- Lab of Molecular Biology, Cambridge, CB2 0QH, United Kingdom; Lab for Molecular Cell Biology, UCL, London, WC1E 6BT, United Kingdom.
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8
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Tiwary AK, Zheng Y. Protein phase separation in mitosis. Curr Opin Cell Biol 2019; 60:92-98. [PMID: 31176175 DOI: 10.1016/j.ceb.2019.04.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Accepted: 04/26/2019] [Indexed: 01/11/2023]
Abstract
Through phase separation, some proteins form liquid-like condensates or droplets which can flow, fuse, and even deform when pressure is applied. In some cases, the condensates 'mature' to form gel or solid-like structure. Recent studies suggest that the liquid-like condensates form the structural basis for several membrane-less subcellular organelles such as stress granules and other subcellular structures. Here, we review and discuss studies that implicate protein phase separation in the function of the spindle apparatus and centrosomes.
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Affiliation(s)
- Ashish Kumar Tiwary
- Department of Embryology, Carnegie Institution for Science, Baltimore, MD 21218, United States
| | - Yixian Zheng
- Department of Embryology, Carnegie Institution for Science, Baltimore, MD 21218, United States.
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9
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Yao C, Wang C, Li Y, Zavortink M, Archambault V, Girton J, Johansen KM, Johansen J. Evidence for a role of spindle matrix formation in cell cycle progression by antibody perturbation. PLoS One 2018; 13:e0208022. [PMID: 30485354 PMCID: PMC6261614 DOI: 10.1371/journal.pone.0208022] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Accepted: 11/11/2018] [Indexed: 12/27/2022] Open
Abstract
In Drosophila it has recently been demonstrated that a spindle matrix in the form of a membrane-less macromolecular assembly embeds the microtubule-based spindle apparatus. In addition, two of its constituents, Megator and Chromator, were shown to function as spatial regulators of spindle checkpoint proteins. However, whether the spindle matrix plays a wider functional role in spatially regulating cell cycle progression factors was unknown. Here using a live imaging approach we provide evidence that a number of key cell cycle proteins such as Cyclin B, Polo, and Ran co-localize with the spindle matrix during mitosis. Furthermore, prevention of spindle matrix formation by injection of a function blocking antibody against the spindle matrix protein Chromator results in cell cycle arrest prior to nuclear envelope breakdown. In such embryos the spatial dynamics of Polo and Cyclin B enrichment at the nuclear rim and kinetochores is abrogated and Polo is not imported into the nucleus. This is in contrast to colchicine-arrested embryos where the wild-type dynamics of these proteins are maintained. Taken together these results suggest that spindle matrix formation may be a general requirement for the localization and proper dynamics of cell cycle factors promoting signaling events leading to cell cycle progression.
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Affiliation(s)
- Changfu Yao
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Chao Wang
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Yeran Li
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Michael Zavortink
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | | | - Jack Girton
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Kristen M Johansen
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Jørgen Johansen
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
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10
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Assembly of Mitotic Structures through Phase Separation. J Mol Biol 2018; 430:4762-4772. [DOI: 10.1016/j.jmb.2018.04.041] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 04/21/2018] [Accepted: 04/30/2018] [Indexed: 01/01/2023]
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11
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Fegaras E, Forer A. Precocious cleavage furrows simultaneously move and ingress when kinetochore microtubules are depolymerized in Mesostoma ehrenbergii spermatocytes. PROTOPLASMA 2018; 255:1401-1411. [PMID: 29564559 DOI: 10.1007/s00709-018-1239-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Accepted: 03/08/2018] [Indexed: 06/08/2023]
Abstract
A "precocious" cleavage furrow develops and ingresses during early prometaphase in Mesostoma ehrenbergii spermatocytes (Forer and Pickett-Heaps Eur J Cell Biol 89:607-618, 2010). In response to chromosome movements which regularly occur during prometaphase and that alter the balance of chromosomes in the two half-spindles, the precocious furrow shifts its position along the cell, moving 2-3 μm towards the half cell with fewer chromosomes (Ferraro-Gideon et al. Cell Biol Int 37:892-898, 2013). This process continues until proper segregation is achieved and the cell enters anaphase with the cleavage furrow again in the middle of the cell. At anaphase, the furrow recommences ingression. Spindle microtubules (MTs) are implicated in various furrow positioning models, and our experiments studied the responses of the precocious furrows to the absence of spindle MTs. We depolymerized spindle MTs during prometaphase using various concentrations of nocodazole (NOC) and colcemid. The expected result is that the furrow should regress and chromosomes remain in the midzone of the cell (Cassimeris et al. J Cell Sci 96:9-15, 1990). Instead, the furrows commenced ingression and all three bivalent chromosomes moved to one pole while the univalent chromosomes, that usually reside at the two poles, either remained at their poles or moved to the opposite pole along with the bivalents, as described elsewhere (Fegaras and Forer 2018). The microtubules were completely depolymerized by the drugs, as indicated by immunofluorescence staining of treated cells (Fegaras and Forer 2018), and in the absence of microtubules, the furrows often ingressed (in 33/61 cells) at a rate similar to normal anaphase ingression (~ 1 μm/min), while often simultaneously moving toward one pole. Thus, these results indicate that in the absence of anaphase and of spindle microtubules, cleavage furrows resume ingression.
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Affiliation(s)
- Eleni Fegaras
- Department of Biology, York University, 4700 Keele St, Toronto, ON, M3J 1P3, Canada
| | - Arthur Forer
- Department of Biology, York University, 4700 Keele St, Toronto, ON, M3J 1P3, Canada.
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12
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Fegaras E, Forer A. Chromosomes selectively detach at one pole and quickly move towards the opposite pole when kinetochore microtubules are depolymerized in Mesostoma ehrenbergii spermatocytes. PROTOPLASMA 2018; 255:1205-1224. [PMID: 29468300 DOI: 10.1007/s00709-018-1214-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2017] [Accepted: 01/18/2018] [Indexed: 06/08/2023]
Abstract
In a typical cell division, chromosomes align at the metaphase plate before anaphase commences. This is not the case in Mesostoma spermatocytes. Throughout prometaphase, the three bivalents persistently oscillate towards and away from either pole, at average speeds of 5-6 μm/min, without ever aligning at a metaphase plate. In our experiments, nocodazole (NOC) was added to prometaphase spermatocytes to depolymerize the microtubules. Traditional theories state that microtubules are the producers of force in the spindle, either by tubulin depolymerizing at the kinetochore (PacMan) or at the pole (Flux). Accordingly, if microtubules are quickly depolymerized, the chromosomes should arrest at the metaphase plate and not move. However, in 57/59 cells, at least one chromosome moved to a pole after NOC treatment, and in 52 of these cells, all three bivalents moved to the same pole. Thus, the movements are not random to one pole or other. After treatment with NOC, chromosome movement followed a consistent pattern. Bivalents stretched out towards both poles, paused, detached at one pole, and then the detached kinetochores quickly moved towards the other pole, reaching initial speeds up to more than 200 μm/min, much greater than anything previously recorded in this cell. As the NOC concentration increased, the average speeds increased and the microtubules disappeared faster. As the kinetochores approached the pole, they slowed down and eventually stopped. Similar results were obtained with colcemid treatment. Confocal immunofluorescence microscopy confirms that microtubules are not associated with moving chromosomes. Thus, these rapid chromosome movements may be due to non-microtubule spindle components such as actin-myosin or the spindle matrix.
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Affiliation(s)
- Eleni Fegaras
- Department of Biology, York University, 4700 Keele St, Toronto, ON, M3J 1P3, Canada
| | - Arthur Forer
- Department of Biology, York University, 4700 Keele St, Toronto, ON, M3J 1P3, Canada.
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13
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Abstract
The spindle matrix has been proposed to facilitate mitotic spindle assembly. In this issue, Huang et al. (2018. J. Cell Biol. https://doi.org/10.1083/jcb.201706103) show that the spindle matrix protein BuGZ is sufficient to form micron-scale compartments that recruit and activate Aurora A, a critical kinase for spindle assembly.
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Affiliation(s)
- Jeffrey B Woodruff
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX .,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX
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14
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Li S, Koe CT, Tay ST, Tan ALK, Zhang S, Zhang Y, Tan P, Sung WK, Wang H. An intrinsic mechanism controls reactivation of neural stem cells by spindle matrix proteins. Nat Commun 2017; 8:122. [PMID: 28744001 PMCID: PMC5526931 DOI: 10.1038/s41467-017-00172-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Accepted: 06/08/2017] [Indexed: 11/09/2022] Open
Abstract
The switch between quiescence and proliferation is central for neurogenesis and its alteration is linked to neurodevelopmental disorders such as microcephaly. However, intrinsic mechanisms that reactivate Drosophila larval neural stem cells (NSCs) to exit from quiescence are not well established. Here we show that the spindle matrix complex containing Chromator (Chro) functions as a key intrinsic regulator of NSC reactivation downstream of extrinsic insulin/insulin-like growth factor signalling. Chro also prevents NSCs from re-entering quiescence at later stages. NSC-specific in vivo profiling has identified many downstream targets of Chro, including a temporal transcription factor Grainy head (Grh) and a neural stem cell quiescence-inducing factor Prospero (Pros). We show that spindle matrix proteins promote the expression of Grh and repress that of Pros in NSCs to govern their reactivation. Our data demonstrate that nuclear Chro critically regulates gene expression in NSCs at the transition from quiescence to proliferation. The spindle matrix proteins, including Chro, are known to regulate mitotic spindle assembly in the cytoplasm. Here the authors show that in Drosophila larval brain, Chro promotes neural stem cell (NSC) reactivation and prevents activated NSCs from entering quiescence, and that Chro carries out such a role by regulating the expression of key transcription factors in the nucleus.
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Affiliation(s)
- Song Li
- Neuroscience & Behavioural Disorders Program, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore
| | - Chwee Tat Koe
- Neuroscience & Behavioural Disorders Program, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore
| | - Su Ting Tay
- Cancer & Stem Cell Biology Program, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore
| | - Angie Lay Keng Tan
- Cancer & Stem Cell Biology Program, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore
| | - Shenli Zhang
- Cancer & Stem Cell Biology Program, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore
| | - Yingjie Zhang
- Neuroscience & Behavioural Disorders Program, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore.,NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 28 Medical Drive, Singapore, 117456, Singapore
| | - Patrick Tan
- Cancer & Stem Cell Biology Program, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore.,Cellular and Molecular Research, National Cancer Centre, Singapore, 169610, Singapore.,Cancer Science Institute of Singapore, National University of Singapore, Singapore, 119074, Singapore.,Genome Institute of Singapore, 60 Biopolis Street, Genome 02-01, Singapore, 138672, Singapore
| | - Wing-Kin Sung
- Genome Institute of Singapore, 60 Biopolis Street, Genome 02-01, Singapore, 138672, Singapore.,Department of Computer Science, National University of Singapore, Singapore, 117417, Singapore
| | - Hongyan Wang
- Neuroscience & Behavioural Disorders Program, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore. .,NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 28 Medical Drive, Singapore, 117456, Singapore. .,Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117597, Singapore.
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15
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Heasley LR, Markus SM, DeLuca JG. "Wait anaphase" signals are not confined to the mitotic spindle. Mol Biol Cell 2017; 28:1186-1194. [PMID: 28298492 PMCID: PMC5415015 DOI: 10.1091/mbc.e17-01-0036] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Revised: 02/23/2017] [Accepted: 03/01/2017] [Indexed: 11/18/2022] Open
Abstract
Inhibitory “wait anaphase” signals derived from unbound kinetochores in a mitotic spindle diffuse into the cytoplasm. These diffusible signals can synchronize anaphase onset of neighboring spindles in multinucleate cells. The extent and activity of these signals are subject to diffusion barriers and cytoplasmic dilution. The spindle assembly checkpoint ensures the faithful inheritance of chromosomes by arresting mitotic progression in the presence of kinetochores that are not attached to spindle microtubules. This is achieved through inhibition of the anaphase-promoting complex/cyclosome by a kinetochore-derived “wait anaphase” signal known as the mitotic checkpoint complex. It remains unclear whether the localization and activity of these inhibitory complexes are restricted to the mitotic spindle compartment or are diffusible throughout the cytoplasm. Here we report that “wait anaphase” signals are indeed able to diffuse outside the confines of the mitotic spindle compartment. Using a cell fusion approach to generate multinucleate cells, we investigate the effects of checkpoint signals derived from one spindle compartment on a neighboring spindle compartment. We find that spindle compartments in close proximity wait for one another to align all chromosomes before entering anaphase synchronously. Synchrony is disrupted in cells with increased interspindle distances and cellular constrictions between spindle compartments. In addition, when mitotic cells are fused with interphase cells, “wait anaphase” signals are diluted, resulting in premature mitotic exit. Overall our studies reveal that anaphase inhibitors are diffusible and active outside the confines of the mitotic spindle from which they are derived.
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Affiliation(s)
- Lydia R Heasley
- Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523
| | - Steven M Markus
- Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523
| | - Jennifer G DeLuca
- Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523
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16
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Sengupta S, Rath U, Yao C, Zavortink M, Wang C, Girton J, Johansen KM, Johansen J. Digitor/dASCIZ Has Multiple Roles in Drosophila Development. PLoS One 2016; 11:e0166829. [PMID: 27861562 PMCID: PMC5115829 DOI: 10.1371/journal.pone.0166829] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2016] [Accepted: 11/05/2016] [Indexed: 12/02/2022] Open
Abstract
In this study we provide evidence that the spindle matrix protein Skeletor in Drosophila interacts with the human ASCIZ (also known as ATMIN and ZNF822) ortholog, Digitor/dASCIZ. This interaction was first detected in a yeast two-hybrid screen and subsequently confirmed by pull-down assays. We also confirm a previously documented function of Digitor/dASCIZ as a regulator of Dynein light chain/Cut up expression. Using transgenic expression of a mCitrine-labeled Digitor construct, we show that Digitor/dASCIZ is a nuclear protein that is localized to interband and developmental puff chromosomal regions during interphase but redistributes to the spindle region during mitosis. Its mitotic localization and physical interaction with Skeletor suggest the possibility that Digitor/dASCIZ plays a direct role in mitotic progression as a member of the spindle matrix complex. Furthermore, we have characterized a P-element insertion that is likely to be a true null Digitor/dASCIZ allele resulting in complete pupal lethality when homozygous, indicating that Digitor/dASCIZ is an essential gene. Phenotypic analysis of the mutant provided evidence that Digitor/dASCIZ plays critical roles in regulation of metamorphosis and organogenesis as well as in the DNA damage response. In the Digitor/dASCIZ null mutant larvae there was greatly elevated levels of γH2Av, indicating accumulation of DNA double-strand breaks. Furthermore, reduced levels of Digitor/dASCIZ decreased the resistance to paraquat-induced oxidative stress resulting in increased mortality in a stress test paradigm. We show that an early developmental consequence of the absence of Digitor/dASCIZ is reduced third instar larval brain size although overall larval development appeared otherwise normal at this stage. While Digitor/dASCIZ mutant larvae initiate pupation, all mutant pupae failed to eclose and exhibited various defects in metamorphosis such as impaired differentiation, incomplete disc eversion, and faulty apoptosis. Altogether we provide evidence that Digitor/dASCIZ is a nuclear protein that performs multiple roles in Drosophila larval and pupal development.
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Affiliation(s)
- Saheli Sengupta
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Uttama Rath
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Changfu Yao
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Michael Zavortink
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Chao Wang
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Jack Girton
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Kristen M. Johansen
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
- * E-mail: (JJ); (KMJ)
| | - Jørgen Johansen
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
- * E-mail: (JJ); (KMJ)
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17
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Kumar G, Kajuluri LP, Gupta CM, Sahasrabuddhe AA. A twinfilin-like protein coordinates karyokinesis by influencing mitotic spindle elongation and DNA replication in Leishmania. Mol Microbiol 2016; 100:173-87. [PMID: 26713845 DOI: 10.1111/mmi.13310] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/13/2015] [Indexed: 11/30/2022]
Abstract
Twinfilin is an evolutionarily conserved actin-binding protein, which regulates actin-dynamics in eukaryotic cells. Homologs of this protein have been detected in the genome of various protozoan parasites causing diseases in human. However, very little is known about their core functions in these organisms. We show here that a twinfilin homolog in a human pathogen Leishmania, primarily localizes to the nucleolus and, to some extent, also in the basal body region. In the dividing cells, nucleolar twinfilin redistributes to the mitotic spindle and remains there partly associated with the spindle microtubules. We further show that approximately 50% depletion of this protein significantly retards the cell growth due to sluggish progression of S phase of the cell division cycle, owing to the delayed nuclear DNA synthesis. Interestingly, overexpression of this protein results in significantly increased length of the mitotic spindle in the dividing Leishmania cells, whereas, its depletion adversely affects spindle elongation and architecture. Our results indicate that twinfilin controls on one hand, the DNA synthesis and on the other, the mitotic spindle elongation, thus contributing to karyokinesis in Leishmania.
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Affiliation(s)
- Gaurav Kumar
- CSIR-Central Drug Research Institute, Jankipuram Extension-10, Sitapur Road, Lucknow, PIN-226 031, India
| | - Lova P Kajuluri
- CSIR-Central Drug Research Institute, Jankipuram Extension-10, Sitapur Road, Lucknow, PIN-226 031, India
| | - Chhitar M Gupta
- Department of Biosciences, Institute of Bioinformatics and Applied Biotechnology, Biotech Park, Electronics City, Phase-I, Bangaluru, PIN-560 100, India
| | - Amogh A Sahasrabuddhe
- CSIR-Central Drug Research Institute, Jankipuram Extension-10, Sitapur Road, Lucknow, PIN-226 031, India
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18
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Jiang H, Wang S, Huang Y, He X, Cui H, Zhu X, Zheng Y. Phase transition of spindle-associated protein regulate spindle apparatus assembly. Cell 2015; 163:108-22. [PMID: 26388440 DOI: 10.1016/j.cell.2015.08.010] [Citation(s) in RCA: 201] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Revised: 06/09/2015] [Accepted: 07/31/2015] [Indexed: 11/24/2022]
Abstract
Spindle assembly required during mitosis depends on microtubule polymerization. We demonstrate that the evolutionarily conserved low-complexity protein, BuGZ, undergoes phase transition or coacervation to promote assembly of both spindles and their associated components. BuGZ forms temperature-dependent liquid droplets alone or on microtubules in physiological buffers. Coacervation in vitro or in spindle and spindle matrix depends on hydrophobic residues in BuGZ. BuGZ coacervation and its binding to microtubules and tubulin are required to promote assembly of spindle and spindle matrix in Xenopus egg extract and in mammalian cells. Since several previously identified spindle-associated components also contain low-complexity regions, we propose that coacervating proteins may be a hallmark of proteins that comprise a spindle matrix that functions to promote assembly of spindles by concentrating its building blocks.
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Affiliation(s)
- Hao Jiang
- State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China; Department of Embryology, Carnegie Institution for Science, 3520 San Martin Drive, Baltimore, MD 21218, USA
| | - Shusheng Wang
- Department of Embryology, Carnegie Institution for Science, 3520 San Martin Drive, Baltimore, MD 21218, USA
| | - Yuejia Huang
- Department of Embryology, Carnegie Institution for Science, 3520 San Martin Drive, Baltimore, MD 21218, USA
| | - Xiaonan He
- State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Honggang Cui
- Department of Chemical and Biomolecular Engineering and Institute for NanoBioTechnology, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
| | - Xueliang Zhu
- State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China.
| | - Yixian Zheng
- Department of Embryology, Carnegie Institution for Science, 3520 San Martin Drive, Baltimore, MD 21218, USA.
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19
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Schweizer N, Pawar N, Weiss M, Maiato H. An organelle-exclusion envelope assists mitosis and underlies distinct molecular crowding in the spindle region. J Cell Biol 2015; 210:695-704. [PMID: 26304726 PMCID: PMC4555823 DOI: 10.1083/jcb.201506107] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2015] [Accepted: 07/28/2015] [Indexed: 01/30/2023] Open
Abstract
A microtubule-independent membranous “spindle envelope” confines spindle assembly and accounts for faithful chromosome segregation. The mitotic spindle is a microtubular assembly required for chromosome segregation during mitosis. Additionally, a spindle matrix has long been proposed to assist this process, but its nature has remained elusive. By combining live-cell imaging with laser microsurgery, fluorescence recovery after photobleaching, and fluorescence correlation spectroscopy in Drosophila melanogaster S2 cells, we uncovered a microtubule-independent mechanism that underlies the accumulation of molecules in the spindle region. This mechanism relies on a membranous system surrounding the mitotic spindle that defines an organelle-exclusion zone that is conserved in human cells. Supported by mathematical modeling, we demonstrate that organelle exclusion by a membrane system causes spatio-temporal differences in molecular crowding states that are sufficient to drive accumulation of mitotic regulators, such as Mad2 and Megator/Tpr, as well as soluble tubulin, in the spindle region. This membranous “spindle envelope” confined spindle assembly, and its mechanical disruption compromised faithful chromosome segregation. Thus, cytoplasmic compartmentalization persists during early mitosis to promote spindle assembly and function.
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Affiliation(s)
- Nina Schweizer
- Chromosome Instability & Dynamics Laboratory, Instituto de Biologia Molecular e Celular, Universidade do Porto, 4150-180 Porto, Portugal Cell Division Unit, Department of Experimental Biology, Faculdade de Medicina, Universidade do Porto, Alameda Prof. Hernâni Monteiro, 4200-319 Porto, Portugal Instituto de Investigação e Inovação em Saúde (i3S), Universidade do Porto, Porto, Portugal
| | - Nisha Pawar
- Experimental Physics I, University of Bayreuth, D-95440 Bayreuth, Germany
| | - Matthias Weiss
- Experimental Physics I, University of Bayreuth, D-95440 Bayreuth, Germany
| | - Helder Maiato
- Chromosome Instability & Dynamics Laboratory, Instituto de Biologia Molecular e Celular, Universidade do Porto, 4150-180 Porto, Portugal Cell Division Unit, Department of Experimental Biology, Faculdade de Medicina, Universidade do Porto, Alameda Prof. Hernâni Monteiro, 4200-319 Porto, Portugal Instituto de Investigação e Inovação em Saúde (i3S), Universidade do Porto, Porto, Portugal
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20
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Nixon FM, Gutiérrez-Caballero C, Hood FE, Booth DG, Prior IA, Royle SJ. The mesh is a network of microtubule connectors that stabilizes individual kinetochore fibers of the mitotic spindle. eLife 2015; 4. [PMID: 26090906 PMCID: PMC4495718 DOI: 10.7554/elife.07635] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2015] [Accepted: 06/18/2015] [Indexed: 12/11/2022] Open
Abstract
Kinetochore fibers (K-fibers) of the mitotic spindle are force-generating units that power chromosome movement during mitosis. K-fibers are composed of many microtubules that are held together throughout their length. Here, we show, using 3D electron microscopy, that K-fiber microtubules (MTs) are connected by a network of MT connectors. We term this network ‘the mesh’. The K-fiber mesh is made of linked multipolar connectors. Each connector has up to four struts, so that a single connector can link up to four MTs. Molecular manipulation of the mesh by overexpression of TACC3 causes disorganization of the K-fiber MTs. Optimal stabilization of K-fibers by the mesh is required for normal progression through mitosis. We propose that the mesh stabilizes K-fibers by pulling MTs together and thereby maintaining the integrity of the fiber. Our work thus identifies the K-fiber meshwork of linked multipolar connectors as a key integrator and determinant of K-fiber structure and function. DOI:http://dx.doi.org/10.7554/eLife.07635.001 Before a cell divides, its genetic material must be copied and then equally distributed between the newly formed daughter cells. In the cells of plants, animals, and fungi, a structure known as the spindle pulls the two copies of the chromosomes apart. The spindle is made up of a network of long, protein filaments called microtubules, and the bundles of microtubules that attach to the chromosomes are referred to as ‘K-fibers’. K-fibers are organized in a way that provides strength. These bundles of microtubules are held together throughout their entire length and, in 2011, it was suggested that a group of proteins including one called TACC3 could cross-link adjacent microtubules within K-fibers. However, it remained unclear how these proteins achieved this. Now, Nixon et al.—including several of the researchers involved in the 2011 work—have used a technique called 3D electron tomography to analyze what holds the K-fibers together in human cells. This analysis revealed struts or connectors that hold together adjacent microtubules within K-fibers. These connectors can vary in size and a single connector can link up to four microtubules. This means that, in a three-dimensional view, the connectors appear as a ‘mesh’ between the microtubules in the bundle. Nixon et al. then increased the levels of the TACC3 protein and found that the K-fibers became disorganized. The spacing of the microtubules with the K-fibers was reduced so that they were more tightly packed than normal. These observations suggest that ‘the mesh’ influences the microtubule spacing within a K-fiber. Nixon et al. analyzed how disorganized K-fibers affected dividing cells and found that it took longer for the chromosomes to move to the newly forming daughter cells. This suggests that cells must maintain optimal levels of TACC3 to ensure that the K-fibers can effectively separate the chromosomes. Further work is needed to identify the other proteins and molecules that make up the mesh. DOI:http://dx.doi.org/10.7554/eLife.07635.002
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Affiliation(s)
- Faye M Nixon
- Division of Biomedical Cell Biology, Warwick Medical School, Coventry, United Kingdom
| | | | - Fiona E Hood
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, United Kingdom
| | - Daniel G Booth
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, United Kingdom
| | - Ian A Prior
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, United Kingdom
| | - Stephen J Royle
- Division of Biomedical Cell Biology, Warwick Medical School, Coventry, United Kingdom
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21
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Qi R, Xu N, Wang G, Ren H, Li S, Lei J, Lin Q, Wang L, Gu X, Zhang H, Jiang Q, Zhang C. The lamin-A/C-LAP2α-BAF1 protein complex regulates mitotic spindle assembly and positioning. J Cell Sci 2015; 128:2830-41. [PMID: 26092935 DOI: 10.1242/jcs.164566] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2014] [Accepted: 06/15/2015] [Indexed: 01/31/2023] Open
Abstract
Some nuclear proteins that are crucial in interphase relocate during the G2/M-phase transition in order to perform their mitotic functions. However, how they perform these functions and the underlying mechanisms remain largely unknown. Here, we report that a fraction of the nuclear periphery proteins lamin-A/C, LAP2α and BAF1 (also known as BANF1) relocate to the spindle and the cell cortex in mitosis. Knockdown of these proteins by using RNA interference (RNAi) induces short and fluffy spindle formation, and disconnection of the spindle from the cell cortex. Disrupting the microtubule assembly leads to accumulation of these proteins in the cell cortex, whereas depolymerizing the actin microfilaments results in the formation of short spindles. We further demonstrate that these proteins are part of a stable complex that links the mitotic spindle to the cell cortex and the spindle matrix by binding to spindle-associated dynein, the actin filaments in the cell cortex and the spindle matrix. Taken together, our findings unveil a unique mechanism where the nuclear periphery proteins lamin-A/C, LAP2α and BAF1 are assembled into a protein complex during mitosis in order to regulate assembly and positioning of the mitotic spindle.
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Affiliation(s)
- Ran Qi
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation and the State Key Laboratory of Membrane Biology, College of Life Sciences, Beijing 100871, China
| | - Nan Xu
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation and the State Key Laboratory of Membrane Biology, College of Life Sciences, Beijing 100871, China
| | - Gang Wang
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation and the State Key Laboratory of Membrane Biology, College of Life Sciences, Beijing 100871, China
| | - He Ren
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation and the State Key Laboratory of Membrane Biology, College of Life Sciences, Beijing 100871, China
| | - Si Li
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation and the State Key Laboratory of Membrane Biology, College of Life Sciences, Beijing 100871, China
| | - Jun Lei
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation and the State Key Laboratory of Membrane Biology, College of Life Sciences, Beijing 100871, China
| | - Qiaoyu Lin
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation and the State Key Laboratory of Membrane Biology, College of Life Sciences, Beijing 100871, China
| | - Lihao Wang
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation and the State Key Laboratory of Membrane Biology, College of Life Sciences, Beijing 100871, China
| | - Xin Gu
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation and the State Key Laboratory of Membrane Biology, College of Life Sciences, Beijing 100871, China
| | - Hongyin Zhang
- Cancer Research Center, Peking University Hospital, Peking University, Beijing 100871, China
| | - Qing Jiang
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation and the State Key Laboratory of Membrane Biology, College of Life Sciences, Beijing 100871, China
| | - Chuanmao Zhang
- The Ministry of Education Key Laboratory of Cell Proliferation and Differentiation and the State Key Laboratory of Membrane Biology, College of Life Sciences, Beijing 100871, China
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22
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Forer A, Johansen KM, Johansen J. Movement of chromosomes with severed kinetochore microtubules. PROTOPLASMA 2015; 252:775-781. [PMID: 25576435 DOI: 10.1007/s00709-014-0752-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Accepted: 12/17/2014] [Indexed: 06/04/2023]
Abstract
Experiments dating from 1966 and thereafter showed that anaphase chromosomes continued to move poleward after their kinetochore microtubules were severed by ultraviolet microbeam irradiation. These observations were initially met with scepticism as they contradicted the prevailing view that kinetochore fibre microtubules pulled chromosomes to the pole. However, recent experiments using visible light laser microbeam irradiations have corroborated these earlier experiments as anaphase chromosomes again were shown to move poleward after their kinetochore microtubules were severed. Thus, multiple independent studies using different techniques have shown that chromosomes can indeed move poleward without direct microtubule connections to the pole, with only a kinetochore 'stub' of microtubules. An issue not yet settled is: what propels the disconnected chromosome? There are two not necessarily mutually exclusive proposals in the literature: (1) chromosome movement is propelled by the kinetochore stub interacting with non-kinetochore microtubules and (2) chromosome movement is propelled by a spindle matrix acting on the stub. In this review, we summarise the data indicating that chromosomes can move with severed kinetochore microtubules and we discuss proposed mechanisms for chromosome movement with severed kinetochore microtubules.
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Affiliation(s)
- Arthur Forer
- Biology Department, York University, North York, Ontario, M3J 1P3, Canada,
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23
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The spindle matrix protein, Chromator, is a novel tubulin binding protein that can interact with both microtubules and free tubulin. PLoS One 2014; 9:e103855. [PMID: 25072297 PMCID: PMC4114980 DOI: 10.1371/journal.pone.0103855] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2014] [Accepted: 07/03/2014] [Indexed: 11/19/2022] Open
Abstract
The chromodomain protein, Chromator, is localized to chromosomes during interphase; however, during cell division together with other nuclear proteins Chromator redistributes to form a macro molecular spindle matrix complex that embeds the microtubule spindle apparatus. It has been demonstrated that the CTD of Chromator is sufficient for localization to the spindle matrix and that expression of this domain alone could partially rescue Chro mutant microtubule spindle defects. Furthermore, the presence of frayed and unstable microtubule spindles during mitosis after Chromator RNAi depletion in S2 cells indicated that Chromator may interact with microtubules. In this study using a variety of biochemical assays we have tested this hypothesis and show that Chromator not only has binding activity to microtubules with a Kd of 0.23 µM but also to free tubulin. Furthermore, we have mapped the interaction with microtubules to a relatively small stretch of 139 amino acids in the carboxy-terminal region of Chromator. This sequence is likely to contain a novel microtubule binding interface since database searches did not find any sequence matches with known microtubule binding motifs.
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24
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Shi C, Channels WE, Zheng Y, Iglesias PA. A computational model for the formation of lamin-B mitotic spindle envelope and matrix. Interface Focus 2014; 4:20130063. [PMID: 24904732 DOI: 10.1098/rsfs.2013.0063] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Recent reports show that, after nuclear envelope breakdown, lamin-B, a component of the nuclear lamina in interphase, localizes around the mitotic spindle as a membranous network. How this process occurs, however, and how it influences mitotic spindle morphogenesis is unclear. Here, we develop a computational model based on a continuum description to represent the abundance and location of various molecular species involved during mitosis, and use the model to test a number of hypotheses regarding the formation of the mitotic matrix. Our model illustrates that freely diffusible nuclear proteins can be captured and transported to the spindle poles by minus-end-directed microtubule (MT) motors. Moreover, simulations show that these proteins can be used to build a shell-like region that envelopes the mitotic spindle, which helps to improve the focusing of the mitotic spindle by spatially restricting MT polymerization and limiting the effective diffusion of the free MTs. Simulations also confirm that spatially dependent regulation of the spindle network through the Ran system improves spindle focusing and morphology. Our results agree with experimental observations that lamin-B reorganizes around the spindle and helps to maintain spindle morphology.
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Affiliation(s)
- Changji Shi
- Department of Electrical and Computer Engineering , The Johns Hopkins University , 3400 North Charles Street, Baltimore, MD 21218 , USA
| | - Wilbur E Channels
- Department of Electrical and Computer Engineering , The Johns Hopkins University , 3400 North Charles Street, Baltimore, MD 21218 , USA
| | - Yixian Zheng
- Department of Embryology , Carnegie Institution of Washington , 3520 San Martin Drive, Baltimore, MD 21218 , USA
| | - Pablo A Iglesias
- Department of Electrical and Computer Engineering , The Johns Hopkins University , 3400 North Charles Street, Baltimore, MD 21218 , USA
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25
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Schweizer N, Weiss M, Maiato H. The dynamic spindle matrix. Curr Opin Cell Biol 2014; 28:1-7. [DOI: 10.1016/j.ceb.2014.01.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Revised: 01/09/2014] [Accepted: 01/11/2014] [Indexed: 10/25/2022]
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26
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Wang C, Yao C, Li Y, Cai W, Bao X, Girton J, Johansen J, Johansen KM. Evidence against a role for the JIL-1 kinase in H3S28 phosphorylation and 14-3-3 recruitment to active genes in Drosophila. PLoS One 2013; 8:e62484. [PMID: 23638096 PMCID: PMC3640051 DOI: 10.1371/journal.pone.0062484] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2013] [Accepted: 03/21/2013] [Indexed: 01/19/2023] Open
Abstract
JIL-1 is the major kinase controlling phosphorylation of histone H3S10 and has been demonstrated to function to counteract heterochromatization and gene silencing. However, an alternative model has been proposed in which JIL-1 is required for transcription to occur, additionally phosphorylates H3S28, and recruits 14-3-3 to active genes. Since these findings are incompatible with our previous demonstration that there are robust levels of transcription in the complete absence of JIL-1 and that JIL-1 is not present at developmental or heat shock-induced polytene chromosome puffs, we have reexamined JIL-1’s possible role in H3S28 phosphorylation and 14-3-3 recruitment. Using two different H3S28ph antibodies we show by immunocytochemistry and immunoblotting that in Drosophila the H3S28ph mark is not present at detectable levels above background on polytene chromosomes at interphase but only on chromosomes at pro-, meta-, and anaphase during cell division in S2 cells and third instar larval neuroblasts. Moreover, this mitotic H3S28ph signal is also present in a JIL-1 null mutant background at undiminished levels suggesting that JIL-1 is not the mitotic H3S28ph kinase. We also demonstrate that H3S28ph is not enriched at heat shock puffs. Using two different pan-specific 14-3-3 antibodies as well as an enhancer trap 14-3-3ε-GFP line we show that 14-3-3, while present in salivary gland nuclei, does not localize to chromosomes but only to the nuclear matrix surrounding the chromosomes. In our hands 14-3-3 is not recruited to developmental or heat shock puffs. Furthermore, using a lacO repeat tethering system to target LacI-JIL-1 to ectopic sites on polytene chromosomes we show that only H3S10ph is present and upregulated at such sites, not H3S28ph or 14-3-3. Thus, our results argue strongly against a model where JIL-1 is required for H3S28 phosphorylation and 14-3-3 recruitment at active genes.
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Affiliation(s)
- Chao Wang
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Changfu Yao
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Yeran Li
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Weili Cai
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Xiaomin Bao
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Jack Girton
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
| | - Jørgen Johansen
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
- * E-mail: (KMJ); (JJ)
| | - Kristen M. Johansen
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
- * E-mail: (KMJ); (JJ)
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